A device for determining the viscosity of fluids is described in German Patent No. DE 24 44 148 A1. In addition to an injector, which has a piston and a hollow cylinder including a nozzle, this device has a cannula and a forward-feed device by which the piston is displaceable at a uniform speed. To calculate the viscosity of a fluid, a pressure sensor measures the pressure of the fluid to be measured directly in front of the cannula through which the fluid to be measured is pressed. This makes direct contact between the pressure sensor and the fluid to be measured unavoidable and also the then required cleaning of the pressure sensor after each measurement.